The central aim of this project is to develop new knowledge about the initiation and sequencing of pro-adolescents and adolescents' use of alcohol, tobacco and other drugs for White, Black, and Hispanic males and females. Our broad, long-term objective is to redirect, reformulate, and fine-tune future intervention and prevention programs for American youth. Using a structural equation approach, special attention will be directed to the antecedents and correlates of first use of the "gateway drugs." This method will supply information about predictors of movement along the drug use sequence from pre-adolescence to young adulthood. Specific aims of this study include: 1) identifying the specific sequences of substance use among a carefully selected, representative sample of youth; 2) comparing the sequences of substance use for White, Black, and Hispanic males and females; 3) specifying predictors associated with initiation and movement along the sequences consistent with a social learning perspective; and 4) contrasting predictors for White, Black, and Hispanic males and females. A cohort-sequential design, similar to that used by Jessor and Jessor (1977), will be used for this study. Data will be collected from elementary, junior high and senior high school students in Lake County, Indiana, over a four year period. Four adolescent cohorts (graduation classes) will be tracked, including the 'Class of 1999," beginning with grade 5 and followed through grade 8, including the transition from pre-adolescence to early adolescence; the "Class of 1997,11 beginning with grade 7 and followed through grade 10; the "Class of 1995," beginning with grade 9 and followed through grade 12, including the transition from middle adolescence to late adolescence; and the 'Class of 1993,11 beginning with grade 11 and followed to two years after graduation, including the transition from late adolescence to young adulthood. Procedures will be used to minimize attrition due to absenteeism and dropouts. Cohort, age and period effects will be examined using several complementary procedures. Structural Equation Modeling (SEM) will be used to test models of adolescent drug use sequencing for the various racial/ethnic and gender subgroups, and to test models of the predictors of drug use initiation and sequencing for these same subgroups.